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c88f369fd3
Bah. It wasn't just the echo that had gotten messed up in the
conversion to the new and more legible pot metadata.
The *new* metadata defaults are pretty clear and obvious, but the old
ones were not, and I clearly should have been a whole lot more careful
in converting them, because half the effects had various messed up
default values. Lots of "zero meant pot at noon - so float value 0.5"
turned into just plain "zero means zero".
So I do think the new model is a lot better, but "Mistakes were made".
I tried to go through every effect and double-check it against what it
used to be. Not that all the old defaults were sane (I'm looking at
you, boost effect), but the metadata conversion wasn't meant to change
them.
Fixes: 9c208692f7 ("Convert effects to metadata-driven boiler plate generation")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
53 lines
2.0 KiB
C
53 lines
2.0 KiB
C
// NAME: Tremolo [TREM]
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// PRIORITY: 110
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// POT: "Rate" FREQUENCY(0.1 10.0) = 2.5 Hz
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// POT: "Depth" LINEAR(0.0 1.0) = 0.5
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// POT: "Mode" ENUM(NORM HARM) = NORM
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// Tremolo: sinusoidal amplitude modulation, NORM and HARM modes.
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//
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// NORM: gain = 1 + k * lfo, where k = depth / (2 - depth).
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// Average gain is exactly 1.0 at all depth settings. At 100% depth,
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// gain swings 0..2; at 50% it swings ~0.67..1.33. Bipolar AM formula
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// (Strymon/Boss-class) rather than one-sided 0..1, which would lose up
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// to 6 dB of average level at full depth.
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//
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// HARM: two independent one-pole filters modelled on the Fender 6G4 harmonic
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// vibrato circuit. Low branch is a 1-pole LP (R=220k, C=5nF, fc≈144.7 Hz);
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// high branch is a 1-pole HP (R=1M, C=250pF, fc≈636.6 Hz, implemented as
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// in - LP at that same corner). These are not complementary crossover halves,
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// so lo+hi has a broad mid-frequency dip (~8 dB at 300 Hz). To avoid that
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// level drop the LFO modulates the difference (lo - hi) added to in, not the
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// branches directly: out = in + k*lfo*(lo - hi). Unity gain at zero depth,
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// same anti-phase modulation character at non-zero depth.
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static struct {
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struct lfo_state lfo;
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float k;
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int harmonic;
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float lp1_a, lp1_z; // one-pole LP at 144.7 Hz (low branch)
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float lp2_a, lp2_z; // one-pole LP at 636.6 Hz; HP = in - lp2 (high branch)
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} tremolo;
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static void tremolo_init(unsigned char pot[10])
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{
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set_lfo_freq(&tremolo.lfo, tremolo_pot0(pot[0]));
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float d = tremolo_pot1(pot[1]);
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tremolo.k = d / (2.0f - d);
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tremolo.harmonic = (pot[2] == 1);
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tremolo.lp1_a = pow2(-9.06472028f * 144.7f / SAMPLES_PER_SEC);
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tremolo.lp2_a = pow2(-9.06472028f * 636.6f / SAMPLES_PER_SEC);
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}
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static float tremolo_step(float in)
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{
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float lfo = lfo_step(&tremolo.lfo, lfo_sinewave);
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if (!tremolo.harmonic)
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return in * (1.0f + tremolo.k * lfo);
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float lo = (tremolo.lp1_z = in + tremolo.lp1_a * (tremolo.lp1_z - in));
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float hi = in - (tremolo.lp2_z = in + tremolo.lp2_a * (tremolo.lp2_z - in));
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return in + tremolo.k * lfo * (lo - hi);
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}
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